In a conventional Rankine cycle apparatus for generating kinetic energy by using working fluid, such as water, the working fluid is heated by a boiler or a heating device to produce high pressure vapor, and the high pressure vapor is used to drive a turbine or pistons for generating the kinetic energy. The vapor used for such driving operation is collected by a water condensing device, wherein the vapor is liquidized which is again supplied to the boiler by the liquid pump. As above the working fluid is circulated in the Rankine cycle apparatus. This kind of conventional apparatus is disclosed, for example, in Japanese Patent Publications Nos. 2003-97222 and 2003-161101.
In the above conventional Rankine cycle apparatus, an electric pump of an electrically driven type is generally used as the liquid pump for circulating the working fluid. Therefore, in the conventional Rankine cycle apparatus, it has been necessary to provide a driving circuit, an electric power supply circuit and so on for driving the electric pump. As a result, the conventional apparatus has a complicated structure and high in cost.